Catalytic sensors have been used to detect flammable gases in some applications. However, catalytic sensors have several shortcomings that limit their performance and accuracy. Disadvantages of catalytic sensors include drift and deterioration due to ageing and poisoning of the catalyst, which may affect a magnitude of response therefrom and, therefore, an accuracy thereof.
Microcantilevers have been demonstrated as gas sensor devices, usually with coatings that attract specific gases. When mass is added to the cantilever, a shift in its resonant frequency can be detected. The change in resonant frequency is proportional to the mass change on the microcantilever. It is also known that an uncoated microcantilever can be used to sense the viscosity and density of a gas. Density and viscosity can be considered in composite by simply observing the resonant frequency shift, which may be proportional to viscous damping (VD), or density and viscosity can be deconvoluted by considering both resonant frequency and quality factor changes (Boskovic 2002).
Also known is the physical relationship between a thermal conductivity (TC) and a density of a gas. This can be exploited to identify certain gases (Groot 1977 & Loui LLNL 2014). However, some gases have overlapping, or nearly overlapping, TC versus density vectors, making it difficult to distinguish these gases from each other. Such a technique is also unable to detect multiple gases in a gas mixture since mixed gases may exhibit a thermal conductivity different than the thermal conductivity of the components of the mixture and can lead to erroneous or unreliable measurement results.
Some gases have TC versus VD vectors that are very similar to air, e.g., oxygen (O2), carbon monoxide (CO), and nitric oxide (NO). Some gases, such as hydrogen sulfide (H2S), cannot be detected at low enough concentrations using the TC versus VD vector alone. Metal oxide semiconductor (MOS) and coated microcantilevers frequently have gas cross sensitivities and may be unable to distinguish between several different gases. As one example, current sensors for flammable and other hazardous gases (e.g., catalytic bed sensors, nondispersive infrared (NDIR) sensors, thermal conductivity sensors) are unable to determine a single property of a given gas or gas mixture and are unable to self-correct an output thereof to determine, for example, a concentration of the gas. Accordingly, in some instances, such sensors may not be able to distinguish between, for example, a first gas having a concentration of 500 ppm and a second gas having a concentration of, for example, 5,000 ppm.
For the foregoing reasons, there is a need for a system and method that overcomes conventional sensor disadvantages and that can reliably detect, identify, and/or quantify gases.